T-6A INSTRUMENT NAVIGATION
Aircrews shall disregard any distance displays from automatically selected DME equipment
when VOR or ILS facilities, which do not have the DME feature installed, are being used for
INSTRUMENT LANDING SYSTEM
The ILS is designed to provide an approach path for exact alignment and descent of an aircraft
on final approach to a runway.
The ground equipment consists of two highly directional transmitting systems and, along the
approach, three (or fewer) marker beacons. The directional transmitters are known as the LOC
and glideslope transmitters.
The system may be divided functionally into three parts:
Guidance information: (LOC and glideslope)
Range information (marker beacon and DME)
3. Visual information (approach lights, touchdown lights, centerline lights, and runway
Compass locators located at the Outer Marker (OM) or Middle Marker (MM) may be substituted
for marker beacons. DME, when specified in the procedure, may be substituted for the OM.
Where a complete ILS system is installed at either end of a runway, the ILS systems are not in
111.95 MHz. Signals provide the aircrew with course guidance to the runway centerline.
The approach course of the LOC is called the front course and is used with other functional parts
(e.g., glideslope, marker beacons, etc.) The LOC signal is transmitted at the far end of the
runway. It is adjusted for a course width (full scale fly-left to a full scale fly-right) of 700 feet at
the runway threshold.
The course line along the extended centerline of a runway, in the opposite direction to the front
course is called the Back Course (BC).
When flying inbound on the BC, it is necessary to steer the aircraft
in the direction opposite the needle deflection when making
corrections from off-course to on-course, unless the aircraft's ILS
equipment includes reverse sensing capability. This "flying away
from the needle" is also required when flying outbound on the
front course of the LOC. Do not use BC signals for approach
1-6 INTRODUCTION TO NAVIGATION SYSTEMS